<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
 
</head>

<body>
  <div id="app">
    <button @click="arr.push(arr.length+1)">新增数组</button>
    <ul>
      <li v-for="item in arr" :key="item">
        {{item}}
      </li>
    </ul>
  </div>
  <script src="./vue.global.js"></script>
  <script>
    const { createApp } = Vue;
    const app = createApp({
      data() {
        return {
          arr: [1,2,3,4]
        }
      },
      // 给config 定义 watch属性
      watch: {
        arr: {
          handler(newVal) {
            console.log('数组改变了', newVal);
          },
          deep: true,
          // 初始化 立即触发一次
          immediate: true
        }
      }
    })
    app.mount('#app')
  </script>
</body>

</html>